P38 part.What is this and what does it do????

Ok, so you are standing in front of a 1998 P38 2.5 DSE looking at the engine bay. Look to the back left and there is what looks a green hand grenade on top of something.

What is it, What does it do and should it buzz and whirr for about 30 seconds when turning the ignition to on?

Recently, when turning the ignition to on I get all sorts of fault warnings coming up. Air bag fault, traction control fault alternator fault and ABS fault along with the corresponding coloured lights. If I turn the key back, remove it from the ignition then put it back in it sometimes goes away. The other day I started the engine anyway, and noticed that when the buzzing and whirring form the afore mention part stopped then the fault light went out.

Im sure it is something to do with the brakes as once I lost all braking and the brake pedal went to the floor!! Luckily I hadn't even moved so locked her up again came back the next day, started it up and the fault had gone. Had it checked anyway and there were no faults recorded (surprised surprise) and the brakes were fine.

Another time, when the part was initially whirring and buzzing and the faults were bleeping and flashing I slowly drove off. Sure enough after about 30 seconds the faults warning and lights disappeared one by one much the same as the yellow and red brake lights go out after about 20 yards!

So can anyone tell me what this part is, what is does, why it whirrs and buzzes and could it be throwing up these other "faults"

Many thanks in advance.

Sounds like your ABS brake accumulator (altough i thought they were all black)?
It should run for a few seconds (approx 20 seconds) when you first start up, during whichj time you will have the warning lights illuminated & should run every 3-4 brake pedal presses. If it's running pretty much every second brake pedal press your ready for a new accumulator - usually around £90.00. Follow instructions in RAVE for replacing.
The other warning lights your getting are not connected but sound like a typical low battery symptom.

edit:

The ABS light will only go out when your moving more than approx 6mph.

martynv8 said:

edit:

The ABS light will only go out when your moving more than approx 6mph.

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Yep it's the traction lamp that goes out when system reaches minimum operating pressure. Can take up to 40 seconds to go out if car has been stood a while and accumulator is getting tired but still servicable.

Brake accumulator, thanks people. Yes Martin your right, black not green! it runs every time I depress the brake pedal.
As for the battery, it was replaced last January so it "should" still be good, will get that checked out as well but after replacing the accumulator.

Many thanks once again

lfbullitt said:

Brake accumulator, thanks people. Yes Martin your right, black not green! it runs every time I depress the brake pedal.
As for the battery, it was replaced last January so it "should" still be good, will get that checked out as well but after replacing the accumulator.

Many thanks once again

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New battery doesn't necessarily mean it works
Assuming it is fine though, check alternator is charging it at ~14.2V

lfbullitt said:

Brake accumulator, thanks people. Yes Martin your right, black not green! it runs every time I depress the brake pedal.
As for the battery, it was replaced last January so it "should" still be good, will get that checked out as well but after replacing the accumulator.

Many thanks once again

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Accumulator needs replacing, pump should only run about every 5 presses of the brake pedal
Many of the messages you quote can be caused by low battery voltage.
Alternator fault usually means exactly what it say's, either a bad connection to the alternator or a duff alternator. You should see 14.2 volts at the battery after a short time with the engine at 2k rpm.

Thank you Datatek and Tcubed. Will have the voltage checked out when I get the accumulator fixed. Yes it runs every time I depress the pedal so hopefully all will be sorted. Seemed a bit strange though that what with all the flashing warning lights, dashboard warnings, beeping etc, there were no faults recorded on the diagnostic laptop / notebook at the garage where I took it.

Cheers all.

lfbullitt said:

Thank you Datatek and Tcubed. Will have the voltage checked out when I get the accumulator fixed. Yes it runs every time I depress the pedal so hopefully all will be sorted. Seemed a bit strange though that what with all the flashing warning lights, dashboard warnings, beeping etc, there were no faults recorded on the diagnostic laptop / notebook at the garage where I took it.

Cheers all.

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Those faults should all be soft faults that reset when ignition is reset, which is maybe why they don't show up.
Low voltage on a P38 is really scary because it flashes up lots of phantom faults: I had gearbox, traction and ABS when my battery went duff courtesy of the RF receiver.

Accumulator is fairly easy to do as per RAVE

lfbullitt said:

Thank you Datatek and Tcubed. Will have the voltage checked out when I get the accumulator fixed. Yes it runs every time I depress the pedal so hopefully all will be sorted. Seemed a bit strange though that what with all the flashing warning lights, dashboard warnings, beeping etc, there were no faults recorded on the diagnostic laptop / notebook at the garage where I took it.

Cheers all.

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There is no fault directly associated with a duff accumulator.

Datatek said:

There is no fault directly associated with a duff accumulator.

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Isn't the ABS Traction and Handbrake light staying on a sort of passive fault warning of that?

TCubed said:

Isn't the ABS Traction and Handbrake light staying on a sort of passive fault warning of that?

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The ABS/TC lights staying on can be but has got to be really bad.

Datatek said:

The ABS/TC lights staying on can be but has got to be really bad.

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ie never reaching pressure?

TCubed said:

ie never reaching pressure?

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That would be a faulty pump not the accumulator. Even if the accumulator is completely duff the pump will, if in good condition make the pressure, it will just take longer to do so. And run more often.

wammers said:

That would be a faulty pump not the accumulator. Even if the accumulator is completely duff the pump will, if in good condition make the pressure, it will just take longer to do so. And run more often.

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Oh.. so what's the accumulator for? I thought the pump pressurised it and then it delivered pressure to the system..

TCubed said:

Oh.. so what's the accumulator for? I thought the pump pressurised it and then it delivered pressure to the system..

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The accumulator stores pressurised fluid, enough for several full brake applications. It has an internal bladder charged at around 80 bars with Nitrogen. The pump fills the sphere with fluid against this Nitrogen pressure compressing the bladder to give a usable store of high pressure fluid. Even if the accumulator has lost all it's Nitrogen the sphere will still be charged to full pressure if the pump is good and the lamps will go out. But it will take the pump a lot longer to do it. But there would be no reserve pressurised fluid supply, so the pump would run on every brake application.

wammers said:

The accumulator stores pressurised fluid, enough for several full brake applications. It has an internal bladder charged at around 80 bars with Nitrogen. The pump fills the sphere with fluid against this Nitrogen pressure compressing the bladder to give a usable store of high pressure fluid. Even if the accumulator has lost all it's Nitrogen the sphere will still be charged to full pressure if the pump is good and the lamps will go out. But it will take the pump a lot longer to do it. But there would be no reserve pressurised fluid supply, so the pump would run on every brake application.

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Thanks

Is an accumulator only present on big cars, or all cars? I've never heard about outside of Rangie land

TCubed said:

Thanks

Is an accumulator only present on big cars, or all cars? I've never heard about outside of Rangie land

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It's peculiar to the WABCO system Westinghouse Air Brake Co.

Cheers chaps, just caught up with this. So the "accumulator" is the grenade shaped object and that sits on the "pump". How do I tell which part is / maybe at fault? or do I change both as a matter of course? The whirring noise happens every time I depress the brake pedal but having said that the brakes seem fine. Maybe a tad spongy at the top of the peddle but there is no difference in stopping power etc.

Initially, it will take 30-40 seconds for the whirring to stop after start up. Have looked for but not found any leaks etc around the pump / accumulator or in the engine bay or on the floor.

Cheers for all your input, it makes interesting reading.

lfbullitt said:

Cheers chaps, just caught up with this. So the "accumulator" is the grenade shaped object and that sits on the "pump". How do I tell which part is / maybe at fault? or do I change both as a matter of course? The whirring noise happens every time I depress the brake pedal but having said that the brakes seem fine. Maybe a tad spongy at the top of the peddle but there is no difference in stopping power etc.

Initially, it will take 30-40 seconds for the whirring to stop after start up. Have looked for but not found any leaks etc around the pump / accumulator or in the engine bay or on the floor.

Cheers for all your input, it makes interesting reading.

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The noise is the pump running pressurising the accumulator. Did you not take any notice of what i wrote earlier? Your accumulator is knackered change it.